The point is not "java.lang.Double.parseDouble()", is all the different ways to do that and USE that:

  Double.parseDouble(i) ;

  Double.toString(i) ;

  (double)i ;
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Soo, for each basic type in Java we nee to use a class or object of a super type to can convert one type to other. And depending of the level of the origin type to the destiny type we can't use a static method of a class, we need to use type casting.

Note that for each one we nee to catch exceptions. Is just not a simple thing2thing() call! And type convertion shouldn't be an issue, since this a language thing, not a algorithm stuf.